The present invention relates generally to a circuit for adjusting a circuit parameter (e.g., a resistance or capacitance value) of a semiconductor integrated circuit by "zapping," and more particularly, to a circuit of this type in which the adjusted value of the circuit parameter is ascertained prior to zapping, by testing, to thereby attain the target value more precisely, while avoiding damage to surrounding circuitry during zapping.
Generally, in the manufacture of a semiconductor integrated circuit, target values of circuit parameters such as resistance and capacitance are often hard to achieve, due to manufacturing process errors and a variety of other factors. In order to attain target values for a circuit, conventional zapping employs a method by which "zappable" fuses connected in parallel with circuit trimming components are blown (commonly referred to as "metal zapping") or Zener diodes connected in parallel with the circuit trimming components are shorted out (commonly referred to as "Zener zapping").
FIG. 1 illustrates an exemplary conventional circuit for circuit parameter adjustment using metal zapping.
With reference to FIG. 1, a conventional circuit for achieving a predetermined target value (here, a resistance) of a circuit (here, a resistor network) between nodes X and Y is comprised of resistors R.sub.1, R.sub.2 and R.sub.3 serially connected between nodes X and Y, metal zapping pieces M.sub.1, M.sub.2 and M.sub.3 connected in parallel with resistors R.sub.1, R.sub.2 and R.sub.3, respectively, and terminals A.sub.1, A.sub.2, A.sub.3 and A.sub.4 connected to respective contact points between the metal pieces and resistors. The metal zapping pieces M.sub.1, M.sub.2 and M.sub.3 are fuses made of a conductive material such as copper or aluminum.
In such a configuration, in order to achieve a given target value between nodes X and Y, high voltage is applied across the terminals A.sub.1, A.sub.2, A.sub.3 and A.sub.4 connected to the respective metal pieces M.sub.1, M.sub.2 and M.sub.3 (which are each connected to a resistive network in a circuit device), to thereby sequentially "zap" the metal pieces until the target value is reached or to simultaneously fuse the metal pieces in accordance with the applied voltage.
FIG. 2 illustrates an exemplary conventional circuit for adjusting a circuit parameter using Zener zapping.
With reference to FIG. 2, the conventional Zener zapping circuit is comprised of resistors R.sub.1, R.sub.2 and R.sub.3 serially connected between nodes X' and Y' Zener diodes Z.sub.1, Z.sub.2 and Z.sub.3 parallel-connected to respective resistors R.sub.1, R.sub.2 and R.sub.3, and terminals B.sub.1, B.sub.2, B.sub.3 and B.sub.4 connected to the circuit at common contact points between the Zener diodes and resistors.
With such a configuration, zapping is performed by shorting respective Zener diodes Z.sub.1, Z.sub.2 and Z.sub.3 sequentially until a target resistance value between nodes X' and Y' is reached, or by simultaneously shorting Zener diodes selected in accordance with the applied voltage.
However, such circuits for adjusting circuit parameters for a semiconductor integrated circuit require a long time for obtaining target values. Further, in such conventional circuits, high voltage or high current is directly applied to network elements, which can cause damage to surrounding circuitry.
In addition, if the target value is not attained by zapping, the once-zapped device is unusable and must be discarded.